This invention relates to vitamin D compounds, and more particularly to pharmaceutical uses for 2-methylene-19-nor-20(S)-1α,25-dihydroxyvitamin D3.
The natural hormone, 1α,25-dihydroxyvitamin D3 and its analog in ergocalciferol series, i.e. 1α,25-dihydroxyvitamin D2 are known to be highly potent regulators of calcium homeostasis in animals and humans, and more recently their activity in cellular differentiation has been established, Ostrem et al., Proc. Natl. Acad. Sci. USA, 84, 2610 (1987). Many structural analogs of these metabolites have been prepared and tested, including 1α-hydroxyvitamin D3, 1α-hydroxyvitamin D2, various side chain homologated vitamins and fluorinated analogs. Some of these compounds exhibit an interesting separation of activities in cell differentiation and calcium regulation. This difference in activity may be useful in the treatment of a variety of diseases as renal osteodystrophy, vitamin D-resistant rickets, osteoporosis, psoriasis, and certain malignancies.
Another new class of vitamin D analogs, i.e. the so called 19-nor-vitamin D compounds, are characterized by the replacement of the A-ring exocyclic methylene group (carbon 19), typical of the vitamin D system, by two hydrogen atoms. Biological testing of such 19-nor-analogs (e.g., 1α,25-dihydroxy-19-nor-vitamin D3) revealed a selective activity profile with high potency in inducing cellular differentiation, and very low calcium mobilizing activity. Thus, these compounds are potentially useful as therapeutic agents for the treatment of malignancies, or the treatment of various skin disorders. Two different methods of synthesis of such 19-nor-vitamin D analogs have been described (Perlman et al., Tetrahedron Lett. 31, 1823 (1990); Perlman et al., Tetrahedron Lett. 32, 7663 (1991), and DeLuca et al., U.S. Pat. No. 5,086,191).
In U.S. Pat. No. 4,666,634, 2β-hydroxy and alkoxy (e.g., ED-71) analogs of 1α,25-dihydroxyvitamin D3 have been described and examined by Chugai group as potential drugs for osteoporosis and as antitumor agents. See also Okano et al., Biochem. Biophys. Res. Commun. 163, 1444 (1989). Other 2-substituted (with hydroxyalkyl, e.g., ED-120, and fluoroalkyl groups) A-ring analogs of 1α,25-dihydroxyvitamin D3 have also been prepared and tested (Miyamoto et al., Chem. Pharm. Bull. 41, 1111 (1993); Nishii et al., Osteoporosis Int. Suppl. 1, 190 (1993); Posner et al., J. Org. Chem. 59, 7855 (1994), and J. Org. Chem. 60, 4617 (1995)).
Recently, 2-substituted analogs of 1α,25-dihydroxy-19-nor-vitamin D3 have also been synthesized, i.e. compounds substituted at 2-position with hydroxy or alkoxy groups (DeLuca et al., U.S. Pat. No. 5,536,713), which exhibit interesting and selective activity profiles. All these studies indicate that binding sites in vitamin D receptors can accommodate different substituents at C-2 in the synthesized vitamin D analogs.
In a continuing effort to explore the 19-nor class of pharmacologically important vitamin D compounds, an analog which is characterized by the presence of a methylene substituent at the carbon 2 (C-2) has been synthesized and tested. Of particular interest is the analog which is characterized by the unnatural configuration of the methyl group at carbon 20 (C-20), i.e. 2-methylene-19-nor-20(S)-1α,25-dihydroxyvitamin D3. This vitamin D analog is disclosed in DeLuca et al U.S. Pat. No. 5,843,928, and its use for treating a metabolic bone disease where it is desired to maintain or increase bone mass is taught therein.
As is commonly accepted, human bones are subject to a constant and dynamic remodeling process which includes bone resorption and bone formation. Bone resorption is based on the destruction of bone matrix, and is controlled by specialized cells known as osteoclasts. Bone formation is accomplished by bone forming cells known as osteoblasts which function to replace the bone resorbed by the osteoclasts.
From childhood through adolescence (i.e. up to about age 20), bone modeling and remodeling is controlled so that skeletal growth is at an accelerated pace in order to match the growth of other body organs. Skeletal accumulation continues through young adulthood (from about age 20 to about age 30) though at a slower rate. In normal healthy mature adults (between the ages of about 30 and about 50 (and in the absence of being pregnant for women) the bone remodeling process will typically be at equilibrium between bone formation and bone resportion. Thereafter, and as the normal consequence of aging, an imbalance in the bone remodeling process develops, resulting in loss of bone. If such imbalance continues over time, bone mass and consequently bone strength is reduced leading to increased potential for fractures.
The majority of metabolic bone diseases are based on an imbalance in the remodeling process, i.e. a disturbed equilibrium between bone resorption and bone formation either from an acceleration of bone resorption activity by osteoclasts or reduction in bone formation activity by osteoblasts. In either event, the result is a decrease in the amount of bone mass and a consequent decrease in bone strength, which ultimately develops into a bone disorder or bone disease. The most common metabolic bone disease is osteoporosis. Osteoporosis is a disease characterized by low bone mass and high bone fragility resulting in an increased risk of fractures. It results from an imbalance in the ongoing bone remodeling process, and due to the extremely complex nature of the remodeling process, it is not easily stopped or reversed.
Osteoporosis can develop as a result of numerous different causes. It is generally categorized as including osteoporosis induced by hormone deficiency (e.g. estrogen deficiency commonly referred to as postmenopausal osteoporosis) and old age (e.g. senile osteoporosis) as well as acquired osteoporosis induced by various drug therapies (e.g. steroid induced osteoporosis as a result of treatment with anti-inflammatory glucocorticoid drugs) and what is referred to as low bone turnover osteoporosis.
Conventional osteoporosis treatment includes, for example, the administration of estrogens, estrogen/progesterone (referred to as hormone replacement therapy), calcitonin, vitamin D analogs, bisphosphonates, parathyroid hormone, and sodium fluoride. Each of such treatments has its limitations due to the multifaceted and complex nature of osteoporosis. In addition, some of such treatments involve serious undesirable side effects which limit their utility.
Osteoporosis, and other diseases characterized by a need to increase the strength of a bone, occur with increasing frequency as humans age, especially after middle age. These types of diseases are some of the most important medical disorders affecting the elderly, and because of the high incidence of fractures and their relatively high costs, their prevention remains one of the major unresolved public health problems facing society. Because bone loss has occurred over many years, and possibly decades, before fractures begin to occur, any drug intervention program aimed at preventing the development of metabolic bone diseases such as osteoporosis should begin earlier rather than later in one's life.